Most chemical reactions of interest for clean energy are routinely carried out in nature. These reactions include the conversion of sunlight to chemical energy, the transfer of carbon dioxide into and out of solution, the selective oxidation of hydrocarbons (including methane to methanol), the formation of C—C bonds (including methane to ethylene), and the formation and dissolution of Si—O bonds (including enhanced mineral weathering). Conventional industrial approaches to catalyze these reactions are either inefficient or have yet to be developed.
Certain enzymes have been identified that carry out each of the aforementioned reactions. Unfortunately, industrial biocatalysis is primarily limited to the synthesis of low-volume, high-value products, such as pharmaceuticals, due to narrow operating parameters required to preserve biocatalyst activity. Enzyme catalyzed reactions are thus typically carried out in fermenters, which are closed, stirred, tank reactors configured to use bubbled gases for mass transfer. FIG. 1, illustrates a conventional stirred tank reactor 100, which may include a motor 102, an input/feed tube 104, a cooling jacket 106, one or more baffles 108, an agitator 110, one or more gas spargers 112, and an aqueous medium 114. Gas exchange in the stirred tank reactor 100 may be achieved by bubbling from the sparger(s) 112 at the bottom of the aqueous medium 114 and gas collection above said aqueous medium 114. Care must be taken to maintain a narrow set of conditions in such stirred tank reactors to favor the desired metabolic pathways and discourage competing pathways and competing organisms. Moreover, stirred tank reactors are energy inefficient, require batch processing, suffer from loss of catalytic activity due to enzyme inactivation, and exhibit slow rates of throughput due to low catalyst loading and limited mass-transfer.
To allow reuse of enzymes in stirred-tank reactors, and to improve stability in reactor conditions, enzymes may be immobilized on inert, artificial materials. As shown in FIG. 2, one conventional approach is to immobilize enzymes 202 on the surface of an inert material 204. Other conventional approaches may involve immobilizing enzymes on the surface of accessible pores of inert materials. However, such conventional enzyme immobilization techniques also suffer from lower volumetric catalyst densities, low throughput rates, and do not have routes for efficient gas delivery or product removal.